SIMULATION OF LASER-PLASMA DYNAMICS - INFLUENCE OF AMBIENT-PRESSURE AND INTENSITY OF LASER-RADIATION

A mathematical model, describing the dynamics of laser plasma (gas dyn amic stage) in air medium with the pressure variation in the range of 1-100 Bar, is presented. The simulation is based on the transient axia lly symmetric system of radiative gas dynamic equations. The applicati on on the multi-group diffusion approximation for the simulation of ra diation transfer is discussed. The solution of gas dynamic equations i s made by the explicit finite-difference FLIC method. For the energy e quation solving jointly with the averaged equation of radiation diffus ion, the implicit difference scheme is used. The later is realized by the proposed nonlinear iterative procedure. The evolution of laser pla sma in the near threshold values (for plasma formation) of radiation i ntensity G = 5 x 10(7)-5 x 10(8) W/cm2 (lambda = 1.06 mum) is analyzed . It is shown that the mechanism of the plasma expansion strongly depe nds on the pressure of the gaseous medium: it varies from the light de tonation regime of fast combustion at low pressures; to the slow combu stion in the form of the subsonic radiative wave at high pressures. (C ) 1994 Academic Press, Inc.